321.233 Road workers exempted.

This chapter, except sections 321.277 and 321.280, does not
apply to persons and motor vehicles and other equipment while
actually engaged in work upon the surface of a highway
officially closed to traffic but does apply to such persons
and vehicles when traveling to or from such work. The minimum
speed restriction of section 321.285, subsection 6, and the
provisions of sections 321.297, 321.298, and 321.323 do
not apply to road workers operating maintenance equipment
on behalf of any state or local
authority while engaged in road maintenance, road blading,
snow and ice control and removal, and granular resurfacing
work on a highway, whether or not the highway is closed to
traffic.